But that's pretty sad. The guy was forced to resign because he peacefully oppose gay marriage?

Not sad at all.

Eich was not qualified to be Mozilla's CEO. They are not a for-profit company existing to make money for shareholders. They are a non-profit organization existing to fulfill an innately social and ethical mission. Eich gave both his voice and tangible resources in the form of money to deny equal treatment under law to gay Americans. People within Mozilla and without rightly, in turn, voiced their opinion that he was not fit to hold the role of CEO for that reason. They were right.

Intolerance of intolerance isn't intolerance. Slowly but surely over the centuries our society is getting closer to giving equal treatment under law to all citizens...minorities, women, LBGT. We have a long way to go yet, but it isn't a sad day when a bigot doesn't get the high-profile job he wanted because because of his bigotry, not matter how civilly he wraps his words or frames his actions. It is right and good that people called him on this and the organization which exists for an ethical purpose recognized how unethical his actions were and his own refusal to justify them, and showed him the door. This has nothing to do with his 1st amendment rights or government censorship. He publicly held a stance and took certain actions that were deemed blatantly immoral by a large portion of the public and got called on.